The cognitive efficiency of 14 divers was studied during 1-hour exposure to water of 40°F (4.4°C) and 78°F (25.6°C). Reasoning ability was tested using a sentence comprehension task presented at the beginning and end of each test session. Vigilance was tested by requiring subjects to detect the onset of a faint peripheral light during the performance of a two-man pipe assembly task. Memory was tested by requiring subjects to learn a number of “facts” during the dive, with retention tested by recall and recognition on land, after a 40-min delay. Despite a mean drop in rectal temperature of 1.3°F (0.72°C), neither reasoning nor vigilance was impaired. Memory performance did deteriorate, though it is suggested that this may reflect a peripheral context-dependent memory effect. It is concluded that a well-motivated subject may be cognitively unimpaired despite a marked drop in deep body temperature.

It was hypothesized that in diving, danger-induced stress may contribute to performance decrement by narrowing perceptual scope. A study was conducted to examine the effect of task load and type of underwater exposure on response time to a signal light in the visual periphery. Novice divers monitored a peripheral light alone, or while simultaneously performing a central addition or dial-watching task. Each subject was tested on the surface, in a diving tank, and in the open ocean. It was found that the central tasks did not interfere with peripheral vigilance on the surface. During diving, a distinct subgroup of the dual-task subjects exhibited markedly increased response times to the peripheral light while maintaining near constant performance on the central tasks. Their behavior appeared more closely related to diving risk than to other environmental factors. The remaining dual-task subjects, and the light alone group, were almost uneffected by underwater exposure. The hypothesis was considered partially validated.

In this study, 15 male subjects performed a central visual acuity task (Landolt ring detections) and a peripheral light detection task during what they thought to be a 60-ft. dive in a pressure chamber. There was no actual pressure change. A 15-man control group performed the same tasks at an outside location. Experimental measures included a posttest anxiety checklist and continuous heart rate recording. The chamber group showed significantly higher anxiety scores and also a significantly higher heart rate throughout the experiment. There was no difference between the groups with regard to correct Landolt detections, although the chamber group responded somewhat slower. Peripheral detection, however, was severely and significantly degraded in the chamber group. It was concluded that perceptual narrowing had been demonstrated as a result of psychological stress associated with exposure to the “dangerous” pressure-chamber.

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